We have long been involved in elucidating the metabolic pathways for both biosynthesis and degradation of several acyclic sugar alcohols, e.g., sorbitol and mannitol, and determining the characteristics and tissue, cell, and subcellular locations of those enzymes involved in these pathways. Enzyme identification and characterization currently includes study of regulatory mechanisms at both the protein and gene level. We have, for example, cloned and sequenced the gene for mannose 6-phosphate reductase, a key step in mannitol biosynthesis, and are now investigating those factors involved in its regulation. For our work on mannitol metabolism in plants we initially used MALDI-MS to verify less accurate molecular weight determinations of the enzyme mannose 6-phosphate reductase (M6PR). Following gene cloning, MALDI-MS also confirmed clonal identity by allowing a comparison of the molecular weights of the clonally expressed bacterial and the native plant enzymes. The importance of this work relates to plant stress physiology. We are very interested in developing an understanding of the mechanisms by which plants tolerate abiotic stress, environmental extremes such as salinity, drought, and temperature, especially since several of these mechanisms may be related to the capacity of some plants to synthesize compatible solutes like the acyclic sugar alcohols. Accordingly, we have been looking at how certain abiotic stresses regulate sugar alcohol metabolism, storage, and transport, and how these compounds may accumulate in response to exposure to stress. M6PR along with several similar enzymes in other plants is a key step in acyclic sugar alcohol biosynthesis. Engineering plants with a gene for M6PR can have important implications for developing plants with improved stress tolerance.